Radiant firebox configurations in prior art furnaces produced non-uniform heating of the tubes which led to an increase of the surface area required for radiant heating. Also, some arrangements in prior art furnace designs resulted in a difficult radiant tube replacement. Further, prior art furnaces with multiple services required complex controls or shutdown systems to protect furnace components during all operating conditions. In addition, burner arrangement in prior art furnaces leads to complicated combustion air duct configurations which restrict access for operation and maintenance. It would be desirable to be able to provide a furnace design with multiple cell configurations to allow for separate services in each cell, in turn allowing increased flexibility in the firing which facilitates keeping the furnace within its design limits during startups, shutdowns and emergency situations. The use of multiple firing locations would allow for increased flexibility in maintaining process and utility temperatures while allowing for better fuel utilization and efficiency. It would also be desirable to employ a minimum number of combustion air ducts to simplify the design of the combustion air control system.
U.S. Pat. No. 5,500,034 to Martin discloses a process furnace using vertical, U-shaped wicket coils with multiple side burners. Each U-shaped vertical tube has a single pass in the radiant heating section between inlet and outlet manifolds.
U.S. Pat. No. 3,768,980 to Andersen discloses a furnace with catalyst-filed vertical tubes disposed in twin radiant cells with multiple sidewall burners on either side of the tubes. An inlet manifold distributes process fluid to the tube heads from above the chamber roof through inlet pigtails, and straight pipes connect the two bases to a lower outlet manifold. In this single-pass arrangement, the long and bent pigtails are said to have been replaced by short, straight pipes which can still absorb the individual bending of the vertical reactor tubes, and all other stresses are said to have been eliminated through a suspension system attached to the tube bases.
Perry's Chemical Engineer's Handbook, 6th Edition, pages 9-60 through 9-63 (1984) relates the principal classification of fired heaters according to the orientation of the heating coils in the radiant section, that is, whether the coils are vertical or horizontal. Various vertical-tube fired heaters include vertical-cylindrical, all radiant; vertical-cylindrical, helical coil; vertical-cylindrical, with cross-flow-convection section; vertical-cylindrical, with integral-convection section; arbor or wicket type; and vertical-tube, single-row, double-wall fired.
As far as applicants are aware, the prior art does not disclose a process stream preheating furnace using multiple horizontally separated vertical radiant cells with a plurality of top supported, bottom guided, single row, multiple pass, vertical radiant coils fired on opposite sides by floor-mounted vertical upshot burners.